Cementing compositions and concretes and mortars derived therefrom

ABSTRACT

Concretes and mortars having improved mechanical properties and resistance to chemicals are obtained by incorporating vinyl polymers or copolymers into cementing compositions and effecting curing (after a period of initial setting) at an elevated temperature.

AU 116 EX Duncan et a1.

[ Nov. 26, 1974 1 1 CEMENTING COMPOSITIONS AND CONCRETES AND MORTARS DERIVED TI-IEREFROM [75] Inventors: Frederic James Duncan; Ronald George Chappell, both of Runcorn, England [73] Assignee: Imperial Chemical Industries Limited, London, England 221 Filed: Mar. 20, 1973 [21] Appl. No.: 343,169

[30] Foreign Application Priority Data Apr. 13. 1972 Great Britain 1. 17069/72 [52] US. C1. 106/90 [51] Int. Cl C04b 7/02 [58] Field of Search 106/90 [56] References Cited UNITED STATES PATENTS 3.021.291 2/1962 Thiessen 260/25 3,030,664 4/1962 Sodertalje .4 18/475 3,042,643 7/1962 Foster i A 260/297 3.487.038 12/1969 Toy et al r 4 260/297 3538036 11/1970 Peters et al. .7 260/296 FOREIGN PATENTS OR APPLICATIONS 1,313,268 4/1973 Great Britain 1,111,697 5/1968 Great Britain .4 106/90 938,567 10/1963 Great Britain 106/90 248,033 3/1926 Great Britain 106/90 165,399 1962 U.S.S.R 106/90 Primary ExaminerDelbert E. Gantz Assistant Examiner--John P. Sheehan Attorney, Agent; or Firm-Cushman, Darby & Cushman [57] ABSTRACT (mates and ms having improved mechanical properties and resistance to chemicals are obtained by incorporating 'mers or cogglvmers into cementing compositions an effecting curing latter 21 period of initial setting) at an elevated temperature.

16 Claims, No Drawings CEMENTING COMPOSITIONS AND CONCRETES AND MORTARS DERIVED THEREFROM This invention relates to concretes and mortars. More particularly, it relates to concretes and mortars derived from cementing compositions incorporating polymers and copolymers derived from polymerisable vinyl compounds.

It is nown to in te ol meric aterials in Portland cement compositions in order to impart greater mechanical strength to concretes and mortars derived therefrom. Polymers previously used for this purpose include polyvinylacetate and styrene/butadiene copolymers, but the known methods of preparation of compositions containing such polymers, wherein curing is carried out at substantially ambient temperature, may give rise to concretes and mortars having poor chemical resistance. in the specification of our UK Pat. No. 970,334 there are described certain cementing compositions comprising Portland cement and at least one copolymer of (a) vinyl chloride and/or vinylidene chloride and (b) acrylic or methacrylic esters derived from aliphatic alcohols having from i to 6 carbon atoms; the curing of the said compositions is described as being carried out at 21C.

We have now found that concretes and motars having improved mechanical properties and resistance to chemicals, as well as good weathering properties, may be obtained by ingggporating vinyl polymers and co- W cementing compositions provided that the curing of the cementing composition ismmw '0 I u ature.

Thus according to the present invention there is provided a method of preparation of a concrete or mortar which comprises curing a cementing composition comprising a water-insoluble polymer or copolymer derived from one or more polymerisable vinyl compounds, the curing being effected, after a period of initial setting, at a temperature of at least 40C.

Suitable polymers and copolymers which may be incorporated in the cementing composition include those derived from acrylic esters. methacrylic esters, vinyl acetate, vinyl chloride, vinylidene chloride, styrene, acrylonitrile, butadiene and vinyl esters of long chain carboxylic acids (e.g., carboxylic acids containing 8 to 12 carbon atoms). lti p referred to u se alkyl late/alk l metmqylate cgpglyrflrjll for example those having from 1 to 8 carhomatems' in the alkyl group, but other copolymers which'may be used include styrene/acrylic ester and styrene/butadiene copolymers. It is especially preferred to use the homopo ymers of methyl methacrylate or the copolymers of methyl methacrylate and Z-ethylhexyl acrylate.

The polymers or copolymers may also comprise the residue of an ethylenically unsaturated carboxylic acid copolymerisable with the basic polymers. The acids may vary according to the particular polymers or copolymers, but suitable acids for use in the acrylic/methacrylic ester polymers and copolymers include acrylic acid, methacrylic acid and itaconic acid. An especially preferred copolymer comprises methyl methacrylate, 2-ethylhexyl acrylate and acrylic acid.

The polymers and copolymers preferably have glass transition temperatures (T of at least lC, especially 20C or higher. For thermoplastic copolymers the glass transition temperatures may be calculated from the weight fractions of monomers present in the copolymer and the glass transition temperatures of the homopolymers of the monomers. The glass transition temperatures may be calculated by the known methods and particularly by the simplified equation where W W W, are the weight fractions of monomers l, 2 n present in the copolymer, and T T T are the glass transition temperatures of the homopolymers of monomers l, 2 .....n, and T is the glass transition temperature of the copolymer. Thus our preferred copolymer of methyl methacrylate and ethylhexyl acrylate may vary in glass transition temperature according to the relative proportions of polymethyl methacrylate (T of 105C) and polyethyl hexyl acrylate (T of C). In general, the mechanical strength (e.g., compressive strength) of the resultant concrete or mortar will increase with an increase in the glass transition temperature of the polymer or copolymer used, subject to the proviso that a polymer or copolymer of higher glass transition temperature will require either a higher temperature of curing or a longer curing time.

The cementing composition may comprise materials conventionally used in the production of concrete and mortar, for example hydra li oements (for example Portland cement) and aggregates, for example sand and gravel. Reinforcing materials, for examplejms materials, may also be incorporated.

The proportion of polymer or copolymer (calculated on a dry basis) incorporated into the cementing composition is preferably in the range 5 percent to 50 percent, especially 15 percent to 35 percent, by weight based on the weight of the cement component of the composition. In general, the mechanical strength (e.g., compressive strength) of the resultant concrete or mortar increases with an increase in the proportion of polymer or copolymer in the cementing mixture.

The aforesaid polymers or copolymers may be incorporated into the cementing composition as a waterdispersible dry solid (as prepared, for example by conventional emulsion polymerisation followed by spray drying). Alternatively, emulsion polymers or copolymers may be incorporated as such into the cementing composition. It will be understood that the emulsion polymers and copolymers may contain ingredients which are used in the well-established techniques involving polymerisation of the monomer or monomers in an aqueous medium. Such ingredients include catalysts (for example ammonium persulphate, alkali metal persulphates), surfactants chosen to promote the production of a stable emulsion, and buffering agents (for example alkali metal or ammonium carbonates). An antifoaming agent may also be advantageously incorporated in the emulsion polymer or copolymer to reduce the occlusion of air in the concretes and mortars subsequently produced.

The temperature and duration of heating in the curing stage may be varied within wide limits, but in general concretes and mortars of increased strength are obtained at higher curing temperatures and/or with longer curing times. It is preferred to use a curing temperature of at least 50C, for example in the range 50C to 200C, especially in the range 70C to 160C. It is especially preferred to use a temperature of C or above. The upper limit of temperature will be dependent on the particular polymer because of the risk of thermal degradation to certain polymers at higher temperatures. The actual temperatures adopted will depend on the glass transition temperature of the polymers incorporated into the cementing composition (polymers or copolymers with higher glass transition temperatures require higher curing temperatures) and on the increase in mechanical strength required of the resulting concretes and mortars. The duration of heating is preferably at least 12 hours (conveniently from 12 to 72 hours) but shorter or longer periods may be used if desired according to temperature of curing and the increase in mechanical strength required in the concrete and mortars. Thus, for example, when the curing temperature is 90C or higher, a beneficial effect may in some cases be obtained when the duration of heating is 4 hours.

Concretes and mortars may conveniently be prepared by mixing cement, aggregates and a previously prepared emulsion (or particulate water-dispersible solid) polmcopolymer, for example in a concrete mixer, and then adding further water ifdesired. The aggregates which may be used include any coarse or finegrained materials known in the processing of concrete,

for example sand or gravel.

e minimu 'nitial setting will depend upon the particular cementing composition and may readily be determined by trail. in general, it is preferred to allow the composition to stand for at least 12 hours (conveniently at substantially ambient temperature) before carrying out the final curing.

The concretes and mortars thus produced have high compressive and tensile strengths and show good resistance to attack by water and chemicals, e.g.. hydrochloric acid and aqueous sulphate solutions. The said concretes and mortars find particular application in the manufacture of shaped articles in the form of precast units, e.g., pipes facing panels, beams and flooring sections, and also'in the form ofiightweight building materials. e.g., lightweight lime/sand buildin g blocks.

The invention isillustrated by the Tollowing Examples. Parts and percentages are by weight unless otherwise stated.

Compressive strengths throughout are quoted in the units meganewtons per square metre (MN/m l Mn/m 145 lb/in".

Example l Cement mortars were prepared to the following formulations, using an aqueous dispersion of an emulsion copolymer of 75.5% methyl methacrylate, 22.571 2- ethylhexyl acrylate and 271 acrylic acid (by weight).

The water content was controlled to give mortars of similar consistency. The calculated T of the copolymer is C.

The test blocks (2% in X 1% in X 1% in) were prepared by mixing the polymer dispersion, water and defoamer, and adding this mixture to the cement and sand. After thorough mixing, the mortar was placed in moulds, covered to prevent evaporation of water, and stored for 1 day at approximately 20C to allow initial setting prior to removal from the mould.

Blocks prepared according to formulation 1 were covered and stored at approximately 20C till the compressive strength was determined after 7 or 28 days by use of a hydraulic press, the pressure being applied to the 2 /2 in X 1V2 in sides of the blocks.

Blocks prepared according to formulations 25 were heated for ,16 hours at 160C, and the compressive strength was determined 7 or 28 days after heat treatment.

The compressive strengths observed are shown below:

A cement mortar was prepared according to the following formulation, using an aqueous dispersion of an emulsion copolymer of 75.571 methyl methacrylate. 22.5% Z-ethylhexyl acrylate and 2% acrylic acid by weight. The calculated T,,- of the copolymer is 35C.

Cement 100 Sand 300 Polymer dispersion (509; solids) 64.3

Antifoaming agent (as in Example 1) 0.9

Test blocks were prepared as described in Example 1, and, after demoulding, were covered and stored at approximately 20C for 28 days. Blocks were then heated in an oven at 90C, C or 50C for various times. and the compressive strength of the blocks was determined l day after removal from the oven.

Compressive Strength (MN/m) Time from Heating time demoulding (days) (days) 50C 70C C Treatment Treatment Treatment Blocks prepared in the same way, but stored at approximately 20C for 30, 32 and 43 days showed compressive strengths of 39.1, 42.3 and 54.9 MN/m respectively.

Example 3 Cement mortars were prepared according to the following formulation, using aqueous dispersion of various emulsion copolymers.

Cement l00 Sand 300 Polymer dispersion (50% solids) 57.1 Water 3.6 Antifoaming agent (as in Example 1) 0.9

The emulsion copolymers used were prepared from various mixtures of monomers as shown below:

Cement 100 s-.md 300 Polymer dispersion (50% solids) 57.1

Antifoaming agent (as in Example 1) 0.82

Methyl methacrylate 9g 83 75, (,5 The test blocks were prepared as in Example 1, and if 'h i g 3- after demoulding and curing at approximately C for T(,' (Cl 105 55 35 l0 15-28 days, the test blocks were heated in an oven for 12 hours at 160C. Unmodified cement mortars of similar consistency Test blocks were prepared as tn Example l, and after were prepared at the same time by mixing 50 parts demouldmg were heaed an Oven at 90 C or C 20 water with 100 parts cement and 300 parts sad, and, for 16 hours. The compressive strength was determined after demoulding were Stored at approximately 30 days after heat treatment. f

or 15-28 days.

The unmodified and polymer containing blocks were then tested as described below: Compressive Strength (MN/m) 1 Freeze h t bilit Emulsifirstefiolymer The test blocks ere weighed, and after soaking in 11cm! healing water for 72 hours were subjected to repeated cycles of 1 68A freezing and thawing till 25 percent of the original 2 951) weight had been lost, this being taken as the point of i failure of the test. Throughout the test, the blocks were kept damp by application of water at intervals.

12 unmodified cement mortar blocks were tested, A cement of Similar Consistency was Prepared and of these, one failed after 444 cycles, one after 478 y mixing 50 Parts of water with 100 Parts Cement and cycles, one after 484 cycles and two after 576 cycles. 300 Parts Sand- After curing at approximately for Surface cracks were observed on all 7 unmodified ce- 30 days, the compressive strength was 29.6 MN/m mem mortar blocks after 576 Cycles.

Example 4 In contrast, all 12 polymer-containing blocks were,

' 4O completely free from surface cracks, and showed no Cement mortars were prepared according to the folweight loss after 576 cycles: lowing formulation, using an aqueous dispersion of an 2 Resistance to h drochloric acid emulsion copolymer of 75% Styrene 23% z-ethylhexyl 12 01 mer contaiiiin and 12 unmodified test block acrylate and 2% acrylic acid (by weight). The calcup d g 15 h med To Ofthe copolymer is 31C were weig e an immerse n percent aqueous ydrochloric acid solution. At intervals the blocks were removed from the acid solution and weighed. The average weight losses observed are shown in the table be- Cement IOU Sand .100 Polymer dispersion solids) 57.1 Anlifnaming agent (as in Example 1) L4 50 Time 7: weight loss (days) The test blocks were prepared as in Example 1, and "wdified Unmdified after demoulding, were heated to 90C or 160C for 16 8 23 I hours. The compressive strength was determined 30 14 Tom days after the heat treatment. 30 3 5 disintegration Temperature Compressive Strength 3. Resistance to sulphate solution 90C 100C l2 polymer-containing and 12 unmodified cement NM/m, 7 so I mortar blocks were subjected to repeated cycles of immersion in a 2.1 percent aqueous solution of sodium sulphate for 16 hours and drying for 1 hours at 54C. The length of the test blocks was measured before test- Example 5 ing, and at various times throughout the test. The aver- Cement mortars were prepared according to the folage increase in length is noted below:

7: increase in length (average) Test Cycles Polymer modified Unmodified mortar mortar 12 0.04 0.16 15 0.05 0.19 35 0.05 0.43 82 0.10 Disintegration 170 0.10 250 0.10

Example 6 Cement mortars were prepared by adding aqueous dispersions of various emulsion copolymers, together with water and l2 percent of antifoaming agent (as in Example 1 based on the weight of polymer dispersion, to a mixture of 100 parts of cement and 300 parts of sand. The'cement mortars contained 5.56.9 percent of polymer.

Test blocks were prepared as in Example 1. and, after initial setting at C and demoulding were heated in an oven at 160C for 16 hours. The compressive strength was determined days after heat treatment Copolymer Compressive Strength (MN/m) IO'HMUQU The emulsion copolymers A to H were as follows:-

A Prepared from a mixture of 98% methyl methacrylate and 2% acrylic .acid.

8 Prepared from a mixture of83'/r methyl methacrylate. 15% 2-ethylhexy1 acrylate and 2% acrylic acid.

Example 7 Cement mortars were prepared as in Example 6 using aqueous dispersions of various emulsion copolymers. The quantities of aqueous dispersion and water were adjusted to give a dry polymer content of 8 percent in the cement mortars, and cement mortar compositions of sililar consistency.

Test blocks were prepared as in Example 1 and. after demoulding, were stored for 7 days at approximately 20C. heated in an oven at 90C, 130C or 160C for 16 hours, and stored for a further 7 days at approximately 20C. By way of comparison, some blocks were not heated, but were only stored at approximately 20C for 14 days.

Unmodified cement mortar blocks of similar consistency were prepared at the same time by mixing 50 parts water with parts cement and 300 parts sand and, after demoulding, were stored and heated in the same way as the polymer modified cement mortar blocks.

The blocks were then tested as follows:-

i. The compressive strength was determined, and is shown in the table below.

ii. The resistance to hydrochloric acid was determined by weighing the test blocks and immersing them in 15 percent hydrochloric acid solution. After 4 weeks immersion the blocks were removed from the acid solution and weighed. The percent weight loss is shown in the table below:

iii. The resistance to sulphate solution was determined as described in Example 5. The percent increase in length after 4 weeks (20 cycles) was measured.

Compressive Strength Emulsion Copolymer after after heating at storing at 20C 90C C C 1 43.2 55.2 89.2 101.5 .1 40.0 61.8 81.8 115.) K 56.6 65.3 85.1 111.6 L 5l.1 66.3 77.2 69.0 M as; 49.24 111.1 112.2 N 54.0 59.3 51.1 100.5 21.2 20.2 19.4 19.6

71 weight loss in HCI solution Emulsion Copolymcr after after heating at storing at 20C 90C 130C 190C 1 7.6 5.5 5.0 4.1 J 11.7 8.8 5.9 5.5 K 5.1 3.2 2.4 2.8 L 5.7 4.2 3.1 2.7 M 9.2 11.0 6.3 7.3 N 11.3 11.6 11.0 5.4 disintegrated '14 length increase in sulphate solution Emulsion Copolymer after after heating at storing at 20C 90C 130C 190C 1 0.12 0.04 0.08 0.12 J 0.06 0.00 0.011 0.06 K 0.14 0.08 0.10 0.12 L 0.22 0.18 0.18 0.16 M 0.08 0.02 0.08 0.08 N 0.10 0.16 0.16 0.28 0.18 0.76 0.10 0.10

The emulsion copolymers 1 to N were as follows: 1 Prepared from a mixture of 98% methyl methacrylate and 2% acrylic acid.

J Prepared from a mixture of 75.5% methyl methacrylate, 22.5% 2-ethylhexy1 acrylate and 2% acrylic acid.

K Primal AC73, a thermoplastic acrylic emulsion polymer supplied by Rohm and Haas (UK) Limited.

L Primal AC201, a thermosetting acrylic emulsion polymer supplied by Rohm and Haas (UK) Limited.

M Primal AC658, a thermosetting acrylic emulsion polymer supplied by Rohm and Haas (UK) Limited.

N Primal HA16, a self-crosslinking acrylic emulsion polymer supplied by Rohm and Haas (UK) Lim- Test blocks prepared in the same way, but omitting the heat treatment, were tested 20 days after demould ing; the compressive strength was 69.4 MN/m Example 9 Duration of Heat Treatment (Days) Heat Treatment Test blocks prepared in the same way, but omitting the heat treatment, were tested 19 days after demoulding; the compressive stength was 73.9 NM/m Example 10 ited.

Concrete was prepared as in Example 8, but using an Example 8 aqueous dispersion of an emulsion copolymer of 83% Concrete was prepared to the following formulation, yl m hacrylate. 15% 2-ethy1hexy1 acrylate and using an aqueous dispersion of an emul i copolymer 2 2% acrylic acid. The calculated Tg of the copolymer is of 75.5% methyl methacrylate, 22.5% 2-ethy1hexy1 55C. The compressive strengths observed (measured rylate and 2% acrylic acid by weight. The calculated Tg in MN/m are shown below: of the copolymer is 35C.

Duration of Heat Treatment (Days) Heat Treatment Cement 100 Temperature 7 Sand 200 l 7 Aggregate 400 o Polymer Dispersion (5071 solids) 40 70C 73:8 Wmr 100 c 711.2 90.7 105.7 Antil'ouming Agent 0.6 1322': 109-5 1201 in Example 162 c 10.1.51 1111.2 123.1

Test blocks (4 i che X 4 inches X 4 inches) were Test blocks prepared in the same way, but omitting prepared by adding the polymer dispersion containing the heat treatment, were tested 2022 days after dethe antifoaming agent, and the water to the cementm ding; the compressive r ngth was 66.7 MN/m". /sand/aggregate mixture. After thorough mixing, the concrete was placed in moulds, covered to prevent E xample l 1 evaporat1on of water, and stored for 2 days at approx1- I mately 20C to allow initial setting prior to demoulding. ncr was p p as in Example but ng n The test blocks were stored for 7 days at approximately aqueous dispersion of an emulsion copolymer of 70% 20C and were then heated at 70, 100, 132 or 162C for methyl methacrylate, 28% Z-ethylhexyl acrylate and 1, 2 or 7 days. The compressive strength of the blocks 2% acrylic acid. The calculated Tg of the copolymer is was determined 12-15 days after the start of the heat 20C. treatment. The compressive strengths observed (measured in The compressive strengths (in MN/m) observed are MN/m are shown below: shown below:

Duration of Heat Treatment (Days) Duration of Heat Treatment (Days) Hem Tremmem Heat Treatment Temperature Temperature I 2 7 C 72.4 72.9 84.0 711.2 86.9 103.11 100T 73.11 111,6 9 133C 101.11 105.7 125.11 132C 98.5 112.5 162C 107.0 117.11 124.5 55 162C 90.5 101.4 104.3

Test blocks prepared in the same way, but omitting the heat treatment, were tested 20-22 days after demoulding; the compressive strength was 65.1 NM/m.

Example 12 Cement mortars were prepared to the following formulation, using an aqueous dispersion of an emulsion copolymer of 75.5% methyl methacrylate, 22.5% 2 ethylhexyl acrylate and 2% acrylic acid. The calculated Tg of the copolymer is 35C.

Cement I Sand 300 Polymer Dispersion (50% solids) 57.] Antifoaming agent (as in Example 1) 0.5

Test blocks were prepared as described in Example 1, and, after demoulding, were covered and stored at approximately C for -31 days. The blocks were then heated in an oven at 100C or 134C for various times, and the compressive strength of the blocks was determined 1 day after removal from the oven.

Compressive Strength (NM/m Heating Time (Hours) l34C I00C Treatment Treatment What we claim is:

l. A method of preparation of a concrete or mortar which comprises curing a cement composition comprising:

i. an inorganic cement; and

ii. an aqueous dispersion of a copolymer derived from (a) one or more alkyl acrylates and/or alkyl methacrylates having from 1 to 8 carbon atoms in the alkyl group and (b) an ethylenicallyunsaturated carboxylic acid copolymerizable therewith,

the said curing being effected. after a period of initial setting, at an elevated temperature of at least C.

2. A method according to claim 1 wherein the curing temperature is at least 50C.

3. A method according to claim 2 wherein the curing temperature is in the range 50C to 200C.

4. A method according to claim 3 wherein the curing temperature is in the range C to 160C.

5. A method according to claim 2 wherein the curing temperature is at least C.

6. A method according to claim 1 wherein the curing period at the elevated temperature is at least l2 hours.

7. A method according to claim 1 wherein the period of initial setting is at least 12 hours.

8. A method as claimed in claim 1 wherein the initial setting is effected at substantially ambient temperature.

9. A method according to claim 1 wherein the alkyl methacrylate is methyl methacrylate.

10. A method according to claim 1 employing both an alkyl acrylate and an alkyl methacrylate wherein the alkyl acrylate is Z-ethylhexyl acrylate and the alkyl methacrylate is methyl methacrylate.

11. A method according to claim 1 wherein the.

ethylenically-unsaturated carboxylic acid is acrylic acid or methacrylic acid.

12. A method according to claim 1 wherein there is employed a copolymer of methyl methacrylate, 2- ethylhexyl acrylate and acrylic acid.

13. A method according to claim 1 wherein the copolymer has a glass transition temperature of at least 10C.

14. A method according to claim 13 wherein the copolymer has a glass transition temperature of at least 20C.

15. A method according to claim 1 wherein the proportion of copolymer (calculated on a dry basis) is from 5 percent to 50 percent by weight of the inorganic cement component of the composition.

16. A method according to claim 15 wherein the proportion of copolymer is from 15 percent to 35 percent of the cement component. 

1. A METHOD OF PREPARATION OF A CONCRETE OR MORTAR WHICH COMPRISES CURING A CEMENT COMPOSITION COMPRISING: I. AN INORGANIC CEMENT; AND II. AN AQUEOUS DISPERSION OF A COPOLYMER DERIVED FROM (A) ONE OR MORE ALKYL ACRYLATES AND OR ALKYL METHACRYLATES HAVING FROM 1 TO 8 CARBON ATOMS IN THE ALKYL GROUP AND (B) AN ETHYLRNICALLY-UNSATURATED CARBOXYLIC ACID COPOLYMERIZABLE THEREWITH, THE SAID CURING BEING EFFECTED, AFTER A PERIOD OF INITIAL SETTING AT AN ELEVATED TEMPERATURE OF AT LEAST 40*C.
 2. A method according to claim 1 wherein the curing temperature is at least 50*C.
 3. A method according to claim 2 wherein the curing temperature is in the range 50*C to 200*C.
 4. A method according to claim 3 wherein the curing temperature is in the range 70*C to 160*C.
 5. A method according to claim 2 wherein the curing temperature is at least 90*C.
 6. A method according to claim 1 wherein the curing period at the elevated temperature is at least 12 hours.
 7. A method according to claim 1 wherein the period of initial setting is at least 12 hours.
 8. A method as claimed in claim 1 wHerein the initial setting is effected at substantially ambient temperature.
 9. A method according to claim 1 wherein the alkyl methacrylate is methyl methacrylate.
 10. A method according to claim 1 employing both an alkyl acrylate and an alkyl methacrylate wherein the alkyl acrylate is 2-ethylhexyl acrylate and the alkyl methacrylate is methyl methacrylate.
 11. A method according to claim 1 wherein the ethylenically-unsaturated carboxylic acid is acrylic acid or methacrylic acid.
 12. A method according to claim 1 wherein there is employed a copolymer of methyl methacrylate, 2-ethylhexyl acrylate and acrylic acid.
 13. A method according to claim 1 wherein the copolymer has a glass transition temperature of at least 10*C.
 14. A method according to claim 13 wherein the copolymer has a glass transition temperature of at least 20*C.
 15. A method according to claim 1 wherein the proportion of copolymer (calculated on a dry basis) is from 5 percent to 50 percent by weight of the inorganic cement component of the composition.
 16. A method according to claim 15 wherein the proportion of copolymer is from 15 percent to 35 percent of the cement component. 